1. Field of the Invention
The invention relates to a particle-optical apparatus and a method for operating the same.
The particle-optical apparatus is provided to manipulate a beam of charged particles. The manipulation may comprise guiding and shaping of the beam, and, in particular, deflecting or/and focusing or defocusing the beam at least in one plane.
In particular, the invention also relates to a microscopy system and a lithography system which use of beams of charged particles, such as electron beams for imaging structures.
2. Brief Description of Related Art
From WO 01/22469 A1 there is known a particle-optical apparatus which has an effect of a focusing round lens on a beam of charged particles, wherein an optical axis of the round lens is displaceable transversely to a direction of the beam. To this end, the apparatus comprises two parallel rows of field source members which are spaced apart from each other. The field source members are in each row periodically spaced from each other in a row direction. Source strengths of the field source members are adjusted such that a quadrupole field is provided between the two rows of field source members to manipulate the beam. This quadrupole field cooperates with a field of cylinder lenses provided by slit shaped apertures such that the particle beam is focused with respect to an optical axis which is defined by a position of the quadrupole field in the row direction. By displacing the quadrupole field in the row direction, it is possible to displace the optical axis of the focusing effect also in the row direction.
The optical properties of this conventional particle-optical apparatus have been found to be insufficient.